Self-attaching female fasteners, including pierce and clinch nuts, formed by colder header techniques and secondary press operations, generally include a central pilot portion having an end face including a bore therethrough, an annular flange portion surrounding the pilot portion having a planar panel-supporting end face and an annular groove in the end face of the flange portion surrounding the pilot portion including a bottom wall, an inner side wall surrounding the pilot portion and an opposed outer side wall. Generally, at least one of the inner and outer side walls of the annular groove is inclined toward the other side wall to provide a restricted opening to the annular groove adjacent the end face of the flange portion to improve retention of the fastener following installation in a panel. Further improved retention of the fastener on a panel may be provided by inclining both the inner and outer side walls of the annular groove toward the opposed side wall forming a “dovetail” shaped re-entrant groove. When the panel is deformed against the bottom wall of the groove by a die member or die button having a projecting annular lip configured to be received in the annular groove, the panel is simultaneously deformed beneath the inclined side wall or walls of the annular groove to provide improved retention of the fastener element on the panel. Alternatively, the outer side wall of the annular groove may be inclined toward the pilot portion and the pilot portion may be deformed radially outwardly during installation to provide improved retention as disclosed, for example, in U.S. Pat. No. 6,276,040. However, most installations of self-attaching fasteners also require sufficient torque resistance or anti-rotation means to prevent rotation of the self-attaching fastener on a panel following installation, particularly where the fastener and panel assembly is attached to a second component by a bolt or other male threaded member using a torque wrench or the like.
The prior art discloses various anti-rotation or torque resistant means for self-attaching female fasteners of the type disclosed herein. For example, U.S. Pat. No. 5,531,552 assigned to the predecessor in interest of the assignee of this application discloses forming a plurality of circumferentially spaced protrusions having radial channels therebetween in the bottom wall of the groove which provide improved torque resistance. U.S. Pat. No. 5,549,430 also assigned to the predecessor in interest of the assignee of this application discloses a self-attaching nut of this type, wherein the bottom wall of the groove includes a plurality of circumferentially spaced arcuate or semi-circular protrusions integral with the pilot portion which provide improved torque resistance, but which also deforms panel metal beneath the inclined outer side wall of the annular groove, providing improved push-off strength for the nut and panel installation. U.S. Pat. No. 5,782,594 discloses a pierce nut having a central recess, rather than a groove, having an inner side wall and a plurality of circumferentially spaced radial notches or pockets formed in the panel support face which, when formed by a die member, forms radially inwardly projecting bead like projections in the side wall of the recess, providing improved torque resistance. The above-referenced U.S. Pat. No. 6,276,040 also discloses opposed V-shaped webs integral with the bottom wall of a dovetail-shaped annular groove and the opposed inner and outer side walls of the annular groove. Further, the prior art includes pierce nuts of this type having rectangular ribs or lugs which bridge the bottom wall of the annular groove and are integral with both the inner and outer side walls of the groove as disclosed, for example, in U.S. Pat. No. 6,220,804. However, the pierce nut disclosed in this patent does not have sufficient push-off strength of the pierce nut installed in a panel for many applications and deformation of a panel against ribs integral with the pilot portion causes deformation or distortion of the thread cylinder of a pierce or clinch nut.
As will be understood from the above description of the prior art, there remains a need for a self-attaching fastener particularly but not exclusively including pierce and clinch nuts having improved fastener and panel installation integrity, including push or pull-off strength and torque resistance which avoids distortion of the thread cylinder during installation. The self-attaching fastener and method of assembly of this invention provides improved fastener and panel integrity including improved torque resistance and which avoids distortion of the thread cylinder where the self-attaching fastener is a female fastener, such as a pierce or clinch nut.